The invention relates primarily to the field of acoustical and/or insular building materials, and, more specifically, to such building materials made by wet-forming techniques.
Conventional fiber-based acoustic substrates, such as acoustical ceiling, wall and duct board panels, can either be wet or dry-formed. Acoustic substrates formed by wet-forming techniques generally incorporate short, fine diameter fibers in the formulation. These fibers are compacted by the gravity force of dewatering. It is well settled in the art that compaction, or packing, of fibers has an inverse impact on acoustical absorption performance.
Additionally, conventional wet-formed acoustic substrate formulations require a significant amount of cellulose fiber, e.g. paper fiber, to be incorporated into the substrate formulation in order to achieve sufficient wet-web strength for the material to successfully flow through a wet-form manufacturing process. Due to its chemistry, affinity for water and tendency to hydrogen bond both with water and itself, cellulose fiber has a densifying impact on the wet-formed fiber compositions, which, in turn, limits the level of acoustical absorption that can be achieved by the material. For at least the above reasons, conventional wisdom is that wet-formed fiber based substrates are typically limited in sound absorption capability.
One conventional attempt to overcome this negative impact on acoustic performance has been to add low density foamed materials to the formulation. Though these low density foamed materials provide bulk and thickness to the product which promotes acoustic performance, they fill up the pores of the material, which, in turn, limits the level of acoustical absorption that can be achieved by the material. Presently, the most sound-absorbing wet-formed materials have a porosity of about 90% which, in turn, provides a noise reduction coefficient (NRC) value of approximately 0.75. One widely used low density foamed material is perlite. In addition to the previously mentioned limitation it has on acoustics, perlite, because of its fine cellular pore structure and hydrophilic capillarity, is also difficult and slow to dry.
Additionally, current wet-formed fiber-based acoustic structures are substantially, if not entirely composed of wheel spun fibers, such as mineral fibers, which results in substrates that are generally inflexible, unconformable and high in density, i.e. 12-16 lb/ft3. These substrates which are typically ½ inch to 1 inch thick are friable and break easily. Furthermore, the wet-formed substrates do not absorb impact energy and are easily dented and deformed during handling and/or installation. This is a particular issue with fiber-based acoustical substrates as they posses densities low enough to achieve the limited sound absorption characteristics described above.
At the same time, conventional dry-formed acoustic fiber-based substrates are less dense and highly acoustical and are capable of achieving NRC values typically in the range of 0.80-1.00. Unfortunately, the types of binders compatible with the dry-forming process, including low cost phenol-formaldehyde thermosetting resins and other more expensive reactive thermosetting resins, emit carcinogenic formaldehyde as the resin cures. In addition, these dry-formed products are often inhomogeneous and poorly formed. Further, these resins have associated process and environmental problems. For example, the resins deposit on process equipment, requiring frequent shut-downs and cleaning of the equipment. Phenolic and other thermoset resins used to bind such substrates also do not allow for the molding and embossing of the substrate as the cured binder does not soften and flow when subjected to heat or steam.
Accordingly, there is a need for a product which; delivers high acoustical performance heretofore achieved only in dry-formed materials and which does not possess the aforementioned drawbacks of conventional dry-formed materials.